This invention relates to an arrangement for the preparation of beverages, more especially in a coffee machine, comprising a water reservoir connected in series to a flowmeter, to a pump, to a heating unit and to a hot water outlet opening onto the coffee to be extracted.
Coffee machines with flowmeters are known. For machines such as these, it is important--for maintaining uniformity of size of the cups of coffee produced--to have an electro-valve with a water return pipe to the main reservoir. At present, this electro-valve is situated at the outlet of the heating unit. The mode of operation is as follows: when the machine is actuated, the water arriving from the reservoir passes through the flowmeter, the pump and the heating unit and is returned through the open electro-valve to the reservoir. After a time of about 1 second, the electro-valve is closed and the flowmeter and associated electronics take into account the quantity of water passing through the flowmeter for the size of cup. Now, this positioning of the electro-valve has disadvantages, depending on the moment selected for its closure. If the electro-valve is designed to close when the water has completely filled the heating unit, all the air present in the heating unit will have been returned to the reservoir. On the other hand, the size of cup will certainly always be constant. However, since the present machine is used above all to prepare an espresso coffee, it is now known from experience that, to obtain a good espresso coffee, the extraction water has to be mixed with the air present in the heating unit which gives a coffee having an unctuous and lasting froth. If, by contrast, the electro-valve is designed to close before the water has completely filled the heating unit, a mixture of air and water will effectively be obtained but since, in this case, the exact moment of arrival of the water in the heating unit will not be known, there will be no uniformity in the size of cup during successive extractions.